It has been conventional practice to prepare various textile reinforcing fibers, to be used in contact with rubber compositions, by pretreating them with a rubber latex and a phenol-formaldehyde resin in which the phenol has almost always been resorcinol. This is the so-called "RFL" (Resorcinol-Formaldehyde-Latex) method. Another method commonly used is to generate a resin in situ in the vulcanized rubber-textile matrix by incorporating therein a formaldehyde (or methylene) donor compound, for example, hexamethylene-tetramine or hexa(methoxymethyl) melamine, and a formaldehyde (or methylene) acceptor compound, for example, a dihydroxy-benzene compound, such as resorcinol. This method has been particularly effective where the reinforcing material is brass-coated steel wire, since pretreatment of the wire with the "RFL" system has proven to be largely ineffective. The methylene donor-acceptor method is described by Endter, U.S. Pat. No. 3,517,722.